Gliederung

Objective: Glutathione S-transferases (GSTs) play an important role in multidrug resistance and are upregulated in many tumors including malignant gliomas. Nitric oxide (NO) inhibits growth and induces apoptosis in a variety of cell lines. The diazeniumdiolate prodrug JS-K was designed to generate NO on enzymatic activation by GST targeting the NO effect selectively to GST-overexpressing tumor cells. The antiproliferative effect of JS-K is studied in human U87 glioma cells in vitro.

Methods: Human U87 cells were cultured in a standardized manner and then incubated with JS-K with 8 different doses between 1 and 50 ÂµM for 24h. Cell viability was assessed by MTT assay after 24, 48 and 72 hours to evaluate the time course of the NO effects and the recovery potential of the cells. All experiments were repeated 4 times and done in triplicates. The data was analysed statistically using ANOVA and Student's Newman Keul test.

Results: Exposure of U87 cells to JS-K was highly cytotoxic and showed a linear dose-dependent effect. The IC50 was approximately 30 ÂµM, 25 ÂµM and 20 ÂµM for a 24, 48 and 72 hour culture period, respectively. U87 cells continued to die even after removal of the drug from the culture, possibly by apoptosis induction. No recovery was observed when extending the culture period. A JS-K concentration as low as 1 ÂµM was capable of inducing a significant growth arrest after 72 hours (p=0.03).

Conclusions: This is the first report that the diazeniumdiolate prodrug JS-K which is a potent anticancer drug in leukemia and some gastrointestinal tumors in vivo and in vitro has potent antiproliferative effects in U87 gliomas. Targeting NO release to tumor cells by engineering a prodrug which releases the compound upon cleavage by an enzyme overexpressed in these tumors (GST) might be a new strategy in cancer therapy.